Precise setting of a desired air/fuel ratio in the combustion chambers of the cylinders of the internal combustion engine is particularly advantageous with a view to raw emissions of pollutants by the internal combustion engine which are as low as possible. A substantial contribution to the precise setting of the air/fuel ratio in the respective combustion chambers of the cylinders of the internal combustion engine can be influenced by precise knowledge of an intake pipe pressure in the respective intake pipe of the intake tract of the internal combustion engine.
In this context it is known by means of a physical dynamic model of the intake tract to determine an estimate value of the intake pipe pressure. Such a dynamic physical model is known for example from the specialist book “Handbook Combustion Engine”, published by Richard Basshuysen, Friedrich Vieweg Verlagsgesellschaft mbh, Braunschweig/Wiesbaden, second improved edition June 2002 Pages 557 to 559, the contents of which are hereby incorporated by reference in their entirety.
In addition, implementation of such a dynamic physical model of the intake tract of the internal combustion engine is also known from EP 0 82 0 559 B1, which corresponds to U.S. Pat. No. 5,889,205, the contents of which patents are hereby incorporated by reference in their entirety. Here, a linear relationship in sections is assumed between the fresh gas mass flow and the intake pipe pressure for determining the fresh gas mass flow flowing into the respective combustion chambers. A slope and an absolute term taking into account substantial influence factors are determined as function of the rotational speed, the suction pipe geometry, the number of cylinders, the valve timing and the temperature of the air in the intake pipe. These values are preferably stored in the characteristics of an electronic engine control device. A reduced flow cross section with regard to the throttle flap on the one hand is determined dependent on the throttle flap position and additionally adapted in form of a control circuit depending on a deviation of an estimate value of the intake pipe pressure determined by means of the model and a measured intake pipe pressure.